This invention relates to a method and apparatus for remotely backing up a vehicle's volatile memory. The invention more particularly relates to such a method and apparatus that connects to the vehicle's existing electrical system.
Modern vehicles, such as automobiles, employ a number of microprocessor based electrical subsystems, including engine management systems and accessory subsystems such as radio equipment. A common characteristic of these microprocessor based systems and subsystems is that they employ volatile memory, such as RAM, for storing processor generated data, such as engine management data, or user selected data, such as selected radio channels or time of day. Volatile memory is typically selected for these applications because it is durable and, for storing relatively small amounts of data, it is cost effective. Notwithstanding, a notorious drawback of volatile memory in these applications is that, once power is lost, even for a very short time, the memory's contents are also lost. Solutions to this problem so far have not been entirely satisfactory.
For example, Berger, U.S. Pat. No. 5,569,997, proposes a POWER SUPPLY FOR VOLATILE MEMORY DEVICES AND PORTABLE ELECTRICAL APPLIANCE IN VEHICLES employing a rechargeable battery which is isolated from the vehicle's main battery by a diode. The rechargeable battery is at a lower voltage than the main battery and, therefore, must be connected directly to the 5 volt power inputs of the memory circuits in order to provide back-up power. These power inputs, however, are not generally accessible after the circuit has been incorporated in an electrical subsystem and installed in the vehicle. Therefore, such devices cannot be connected simply to automobile electrical devices, such as radio devices, that are adapted to connect directly to a 12 volt power source and are typically installed after-market.
As another example, Kimura, U.S. Pat. No. 5,375,246, proposes a BACK-UP POWER SUPPLY APPARATUS FOR PROTECTION OF STORED DATA having a switch operable between two positions and selecting either a main battery or a back-up battery having a voltage that differs from the main battery voltage by about a diode drop. For 12 volt automobile systems, a back-up battery voltage of about 12 volts would be required. A disadvantage of a requirement for a 12 volt back-up battery voltage is that higher voltage batteries are generally heavier and take up more space than batteries having lower voltages.
Accordingly, there is a need for a vehicle electrical power back-up circuit and method that provides for ease of connection to electrical subsystems designed for after-market incorporation into the vehicle, and that provides for a savings in weight, bulk and cost over the prior art